Recently, in order to improve the quality of a communication area, a communication system using femtocell base stations has been developed (see, e.g., patent documents 1 and 2).
A femtocell base station is a small radio base station that covers a narrow communication area of some tens meters in radius. The femtocell base station is installed inside a room such as a house, office or the like, in order to cover the communication area inside the room. Use of a femtocell base station makes it possible to improve the communication quality of a communication area that cannot be covered by existing microcell base stations. It is also possible to cover the communication area without incurring costs for installing an infrastructure for microcell base stations.
Further, in recent years, various kinds of products for realizing All-IP networks have been developed. For example, systems have been developed that can accommodate new LTE (Long Term Evolution) networks as well as existing 3G networks defined in 3GPP and further that can accommodate diverse access networks such as WLAN, WiMAX, 3GPP2 and the like.
As a related art document filed by the applicant hereof, for example, patent document 3 (JP2010-252139A) discloses a communication system that is introduced with a femtocell base station using an IMS (IP Multimedia subsystem) network.
The above patent document 3 discloses a scheme in which the subscriber information on a subscriber user (UE) that is managed by the femtocell base station (FAP) is dynamically modified in accordance with the existing position of the subscriber user (UE).